Get the wood burning oven to 210/220 degrees C. Paint the leg of mutton with a little olive oil, season with salt and pepper and put in an oven proof pan. Loosely cover with foil and put in the oven for around twenty minutes.
Meanwhile peel the potatoes and cut into slices around ½cm/¼inch. Peel and thinly slice the onions. Peel and roughly chop the garlic. When the mutton has finished its first cook, take it out the oven. Put fresh rosemary under the mutton, surround the the mutton with layers of potato, onions and garlic lightly seasoning each layer with salt and pepper.
Pour some chicken stock over the potato/onions up to about an inch from the top. Cover with foil and put into the cooling oven at about 275°F/140°C/Reg1 for around four hours, see note on slow cooking in wood burning oven.
Towards the end of the cooking time, wash the samphire under a cold tap and put into a steamer and steam for a few minutes only. When the meat is done take it out and allow to rest for ten minutes or so covered with foil. Drain off any excess liquid from the potatoes and quickly brown under the grill.
Carve slices from the mutton and put on to serving dishes, spoon around some of the potatoes and samphire and serve
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